Calculating tables and the like



Oct. 7, 1952 J. H. STARR 2,613,237

CALCULATING TABLES AND THE LIKE Filed Aug. 27, 1947 5 Sheets-Sheet l IN VEN TOR.

1952 J. H. STARR 2,6 3, 7

CALCULATING TABLES AND THE LIKE Filed Aug. 27, 1947 5 Sheets-Sheet 5 *NeTwork 50585.

Nu IndicuTor Patenteci Oct. 7, 1 952 [UNITED STATES PATENT OFFICE canoonarme TABLES ANDJT-H-E .JamesH; Starr, La Grange, Ill. Allllli'qati'onAugu'stm, 1947, Serial No. 770,850 (CI. 1.71-9.59.

'81 Claims. 1.

Thisinvention relates toimprovements in calculati-ngtables; and the like. The invention concerns itself primarily with improvements in the arrangements and instrument connections and circuits whereby greatly increasedaccuracy of readings may be ensured throughout-the entire range of readings which maybe expected, and withoutthe need of'increasing theaccuracy of the instruments themselves over the accuracies.

2,301,470 issued "November '10, 1'I942',,'f01 Improvements in. Gal'culating Tables and the Like, have. described and claimed improvements which are broadly applicable to all calculating board's; whether operatingfrom direct current orfrom alternating current sources. Genera-11y 'statedthe method and structure disclosed and claimed that 'eariierpatent, and distinguishing over all.

prior art disclosures isthe use of. a current responsive instrument carrying a scale calibrated. in, impedance units as the basis for the :adjust ment of-each of the several impedance simulating elements of the calculating board. commercial form ofthis calculating board the impedance scale is calibrated from 2.00 per unit impedanceto- 0.10 per unit, and circuit changes are a-ccomplished by switching to permit reading impedance down to 0.00 per'unit. The same in strument is used in reading current- "in each branch of theca-lculating board, and for this purpose the instrument carries a second scale 'calibrated in per unit current from 0.00 to 10.00 per unit. This scaleis readable down to 0.20 per unit;

at the-lowest marked scale division.

It is standard commercial practice of instrument-manufacturers to guaranteethe accuracy of electrical instruments by stating the error at any point will not exceed a stated percentage of full scale. Although there are soundreasons for such In the a. method of stating instrument error, it will be appreciated that it results. in. a probable .error which, When-expressed in percent. of actual magnitude, increasesas the magnitude decreases. As

an example, in the. commercial formof. the cal culating board, the calibrated full scale of the-per unit I tcurrent). scale is10.0;per unit, and a;1%f instrument is employed. git-10.0 per unitcurrent the reading will'lie between 9.9 and 10.1 per unit; but if the current measured is actually 1.0 per unit, the reading will lie between 0.9 and. 1.1 per unit. This isa possible error of 10%. However,

if'thecurrent is 0.1 per unit, the reading will liebetween 0.0 and 0.21 per unit. This is an error of 0.1 per unit, amounting to an error of plus or minus and obviously excessive.

In the actual use of the calculating board forthe solution of problems arising in small electric systems, the current in any significant branch may be-expected to beef the order of possibly- 10% of the-total system current. If theoperator by the exercise of judgment and experience, selects a current base such that. the total systemload is-of the order'of 10.0 per unit, the possible error in reading any-individual branch current will be of the-orderof 10%, which maybe acceptable in many cases. In the solution of problems involving: many branches and in which the current in asignificant branch may be as little as 1% of the total system load, the error from this yond theiull scale calibration of the instrument.

The. second? alternative requires that the ca-.

pacityof the battery or otherpower source be increased. to ether with the. current carrying. capacityoi' switches, :rheostats, and other compo.- nents in which the. total systemcurrent may flow.

--At this, point. it maybe noted that an'instrument maybe provided with two or more scales, theadditional scales. providing for adequate deflection and improved accuracy when'measuring current in the smaller branches of the system network. Itis, however, a fact that when the current required to produce full scale deflection of. aninstrument is. reduced, the necessary torque to 'obtainthe desiredrdeflectionmust be obtained by'increasing the number of active turns in the instrumentcoil or by other means. The other meansknown in the art are limited and any sub-- stantia-lreduction in current necessary for full scale. deflection is, substantially, equivalent to a requirement that the resistance of the instru- 3 ment be increased if it be a direct current instrument, or the impedance be increased if the instrument be an alternating current instrument. Such an increase in either resistance or impedance cannot be tolerated in a device of the class described, for the reasons explained below.

In a calculating board constructed as disclosed in the issued Patent No. 2,301,470, the instrument serves two essential purposes. It is connected in circuit with the potential source and an impedance element to permit the adjustment of the impedance element selected to some selected setting within its range as indicated by the per unit Z scale of the instrument. It is also inserted into the various branches of the completed network to permit measurement of the current therein by using the per unit I scale. As a quantitative example, the rhecstats employed as impedance elements in a typical direct current operated calculating board are adjustable over a range of substantially zero to 15,000 ohms. The resistance of the instrument selected is limited to 1.5 ohms maximum, and cannot be reduced substantially below this value except by undesirably increasing the current required for full scale deflection. When a 1.5 ohm instrument is connected in circuit with a 15,000 ohm resistance the change of the resistance of the circuit is only percent of that of the rheostat. But as the setting of the rheostat is reduced the percentage error due to the resistance of the instrument becomes greater. If an error of 1% be established as the maximum acceptable, the rheostat cannot be set below 150 ohms. If a more sensitive instrument be employed, as for example, one requiring the current for full scale deflection, the resistance of the movement of such instrument would be increased from to 20 times the 1.5 ohm value.

If limited to ohms, the rheostat can be set only to values between 1,500 and 15,000 ohms if the error limitation is to be held at 1%. The usable range of the rheostat is thus reduced to 10/1 instead of 100/1 and serious inconvenience in operation would result.

It has therefore been found that when usin the instrument circuit disclosed in my earlier patent, it is necessary to compromise between errors resulting from relatively high instrument resistance (or impedance, in the case of alternating current operated instruments), providingace ceptably large deflections; and errors resulting from undesirably small instrument deflection obtained with an acceptably low instrument resistance (or impedance). This condition has been recognized and circuitconstants have been chosen to obtain the optimum in accuracy and convenience with due regard to cost. been entirely satisfactory for the majority of network studies but cases do occur, particularlyin connection with power systems of large extent, in which it is important that errors due to the above mentioned factors be reduced below the minimum attainable by the best possible se-' lection of circuit constants within commercially practicable limits.

It is evident that the errors above described would be entirely eliminated if it were possible to provide an instrument having multiple scales to cover a wide current range, and having zero resistance (or impedance). 1 have secured the foregoing result by reducing the equivalent resistance (or impedance) of the instrument tov zero, and I have provided means tosecure this 1 result in a calculating board whether direct or alternating current operated. Furthermore, I.

The result has have provided means to secure this result in such calculating boards with further provision for changing the ratio at which the instrument will measure, so that it may be caused to read according to various selected ratios, and with provision for reducing the equivalent resistance (or impedance) v to zero in the case of each such selected ratio. For example, it may be caused to indicate a current equal to that flowing in the branch in which it is inserted, or to indicate 10 times that current, or times that current; as-the operator may select. Errors resulting from resistance (or impedance) of the instrument as well as errors resulting from very small deflection of the instrument pointer, are thus eliminated.

In brief outline my present improvements may be stated as follows:

I provide in a local circuit including the indicating instrument, a local current source, together with local resistances or impedances of known value, to impose an additional amount of current flow through the indicating instrument.

such increase being of known amount or proper.- tion as compared to the value of the current flowing through the network element under test. I provide means for the adjustment of the circuit constants of this local circuit to select one of several available ratios between the current flowing through the indicating instrument and that flowing through the network element under test. 1

between the two voltage drops one of which 18 due only to the current flowing in the network element, and the other of which is due to only the locally generated additional current, and I further provide means to adjust the locally generated additional current to obtain the desired condition of balance. When the desired condition of balance is obtained and indicated by the null indicator which is provided, the-voltage drop due to the current flowing in the network element under test is equal to and opposite to that due to the locally generated current and the net total voltage drop is zero. This condition is equivalent to the insertion of zero resistance (or impedance) in circuit with the network element under test.

- My invention may be further stated to include a method and means by which the error inherent in commercial current responsive instruments at small scale readings, or at small fractions of full scale deflection may be minimized or avoided without introducing additional resistance or impedanoe into the circuit the current in which circuit is being measured. I have herein disclosed several alternative forms of the meanswhereby this and other objects are attained. It

is here noted that the improvements constituting r the present invention ar applicable to calculat' ing boards already constructed and inservice, and which include the features of my earlier, patent,

No. 2,301,470, as well as to calculating boards embodying the features of that earlier patent but which calculating boards have not yet been built. It is further here noted that the improvements of the present invention may be used in or in concurrent snetworks. eccordinglyrll shall; hereinafter disclose; in;detail, -thescircuits and means of thel lpresentzinvention improvementsiin threegerreral-categories, as follows:

} 1. A: structure comprisingan accessory: in.- tended. for: use with existingdirect' current operated calculating boards incorporating the gen eral features :of myzearlier patent, No. 2,301,470.

2. A structure or circuit" modificationv capable of: incorporation or inclusion in new calculating boards" totbe. built embodying. thealfeatures of my earlieripatent Nol,2,301,470, so as. to-directly combine in such new calculating boards the features of the. presentinvention as well as said features of sa'i'd earlier patent. I

A structure or circuit modification capable of incorporation or inclusionin new calculating boards :or as :an accessory to already existing calculating boards, which calculating boards include the features of my 'said earlier patent, 'No. 2-;3'01'A IO, and whichcalculatingboards are for alternating current operation;

It ishere noted that all three of the foregoingcategories to be hereinafter described and illustrated includethefeatures'of'the present invention, and are generically of the same category.

At this point it may be mentioned that in my TI -corresponding to the network element to be tested. In order to adapt the improvements of the present: invention to suchalready constructed calculating boards, I have, as category 1, above listed, provided an accessory'including two cords connected into such accessory and having their free. ends provided with-plugs. suitable for insertion into the openings 21' (as selected) and i0,

respectively; Upon so inserting these accessory plugs this accessory becomes va portion of the calculating board as an entirety, and thereupon the current responsive instrument 1 13 of the calculating boarclas shown in that earlier patent may be usedito read the current in the selected lement of thenetwork; this accessory being itself provided with aninstrument to indicate the "nullf condition under which" said instrument t3 should beread. When incorporating the features of the-present invention into newly built calculating, boards all-switches, rheo-stats, and null indicators, required for theapractice of the presently disclosed improvements willgenerally be built directly intov such newly built calculating boards'as integral portionsthereof.

When using thefeatures of the present invention in or with calculating boards intended for direct current. operation it is evident that no phase difference exists between current and supplied voltage; Consequently it is unnecessary when using direct current sources to make any special provision. for ensuring proper phase position of various voltage drops when reading test instruments. When using alternatin current sources however, it istrue that the voltage drops may differ phase'a-s well as in magnitude. therefore necessary, when using alternating current sources to provide structures capable of a null or balancing adjustment both as to phaseand magnitude. a, current the source should be fixed in frequency,

Therefore when using alternating andideally should be. of pure sine'wave shape:

and this alternating current source should bead justable in phase and in magnitude. Likewise thev null indicator hereinbeiore' referred to, which in the case ofza direct, current source may conveniently be in the form .of a galvanometer, in the case of an alternating current: source must be capable of detecting and indicating to the. operator any condition of unbalance whether due.

to a difference in phase or a difference in magnitude, or both. Furthermore, certain'precautions, are necessary when using an alternating current.

source to ensure that no phase shift errors are introduced by the structure of the improvements herein disclosed, themselves. It is also necessary that the operator be able to determine not only the magnitude of currents and voltages, but the" phase position of these quantities as well. Such provision'I have made in the present invention, as will presently appear in full detail.

Other objects and uses of the invention will appear from a detailed description of the same which consists'in the features of constructionand combinations of parts hereinafter described and claimed.

In the drawings:

Figure 1 shows a typical wiring diagram of a circuit element including the features of the present invention, and in which said circuit element comprises an accessory unit intended for use in connection with a direct current supplied calculating board of the general form shown in Letters Patent of'the United States, No. 2,301,470; and Figure 1 also shows portions of the circuits illustrated in that earlier patent, so as to better i show the relationship between the circuits shown in that earlier patent and the improvements of the present invention;

Figure 2 shows in fragmentary form a portion of the circuits of the improvements shown in Figure 1, with the selector switch in its position to establish a ratioof /1 for the current responsive' instrument;

Figure 3'shows a view'similar to that of'Figure 2, but with the selector switch in its position to establish a 10/1 ratio forthe current responsive instrument;

Figure 4 shows a view similar to those of Figures 2 and 3, but with the selector switch in itsv position to establish a 100/1 ratio for the current responsive instrument;

Figure 5 shows a fragmentary wiring diagram for that portion of the. current responsive instrument circuits needed to embody the features of the presentinvention into a newly'to be built calculating board so that the benefits of the present invention may beprovided by such calculating board;

Figure 6 shows more or. less schematically a portion of the circuits of an alternating current calculating board embodying the features of my earlier patent, No; 2,301,470, together with the features of the present invention and intended for operation on an alternating current sourcer different angular position within the field ele ment;

Figure '7 showsa simplified wiring diagramsimilar to that shown in Figure 6 having provision for adjusting an impedance to any desired value; and

Figure 8 shows a wiring diagram similar to that of Figure '7 with provision for reading current in such impedance element when it forms a part of a complete network.

Fig. 9 shows a portion of the wiring diagram of Fig. 6, wherein provision is made for compensating for the inherent resistance of the inductor.

I shall first describe in detail a typical circuit embodying the features of the present invention as applied in the case of an accessory unit which may be used with the circuit arrangement shown in patent, No. 2,301,470. For this purpose reference may be had to Figure 1 showing a typical accessory unit in its relation to certain elements or' the calculating board shown in said earlier patent; and to Figures 2, 3, and 4 which show in fragmentary form a portion of the circuits of the accessory unit of Figure 1, but with the selector switch moved to its three different positions, as shown in said Figures 2, 3 and 4, respectively.

In Figure 1 I have shown one of the jacks I3 of Patent 2,301,470 and the corresponding variable resistance with its movable contact II; and I have also shown the spring contact It for engagement by the tip of an inserted plug, and the spring contact I5 for engagement by the ring contact of the inserted plug, and also the sleeve contact I4 for engagement by the sleeve of the inserted plug. In this figure I have also shown the jack contact 68, the ring contact 67, and the sleeve contact 65 corresponding to like numbered parts of said earlierpatent. I have also shown the cord IBI having the plug I02 which has the tip contact I03 adapted to engage the contact I0, and also having the contact I04 adapted to engage the ring contact I5, when the plug is inserted into the jack in the well understood manner. Thus the variable resistance of the calculating board is brought into a circuit presently to be described through the medium of the cord MI. I have also in Figure 1 shown a cord I05 having at one end the plug I06 which has the tip contact I01 and the ring contact I08 adapted respectively to engage the contacts 68 and 61 of the calculating board circuit as illustrated in said earlier patent. Thus, with the switch II of that earlier patent moved to its position Branch I, the current responsive instrument 43 of that patent is brought into a circuit including the cord I05. The other end of this cord I05 is provided with a plug I03 having the tip contact H in connection with the tip contact I07, and the ring contact III in connection with the ring contact I have, in this accessory embodiment of the present invention, provided a suitable box-like unit H2 which includes various elements to be presently explained. The cord I3I enters this unit H2. This unit H2 also includes a jack H3 having the tip contact H4 and the ring contact I I which are adapted to be engaged by the contacts H0 and III oi the cord plug I09 already referred to. Thus, when said cord plug is inserted into this jack the cord conductors are continued to the jack contacts H4 and H5, respectively. Thereby, also the current responsive instrument 43 of my earlier patent disclosure is connected into this unit H2.

This unit H2 also includes a three position, four contact switch H6. This switch has the four contacts H1, H8, H9 and I20 which may be simultaneously moved into either one of three positions, corresponding to ratios 1/1, 10/1, and

10071, respectively. For this purpose this switch has the three stationary contacts I2I, I22 and I23, for the movable contact I II; it has the three stationary contacts I24, I25 and I26, for the movable contact I I8; it has the three stationary contacts I21, I28 and I29, for the movable contact I I9; and it has the three stationary contacts I30, I3I and I32 for the movable contact I20.

An impedance element I33 (which may be a simple resistance or other impedance element) is provided for the ratio of 10/1; and another impedance element I34 (which may also be a simple resistance or other impedance element) is .provided for the ratio 100/ 1. Preferably each of these elements I33 and I34 comprises two sections or elements one of which is fixed in value, and the other of which isof variable value so that the combined impedance of each of these elements I33 and I34 may be preset or factory adjusted to an exactvalue in the final adjustment of the unit at the factory. These sections are shown at I33 and I33 and at I34 and I34 respectively. Having been factory adjusted these impedance elements will thereafter correctly ensure the desired ratios, for example, 10/ 1, and 100/ 1, as previously mentioned.

The unit II2. also includes a resistance element or impedance element I35 of variable amount and under control of the operator. This element I35 conveniently comprises the two sections I 35*- and I35 in which case the section I35 may be made of fixed value, and the section l35'= may be of variable or adjustable value, under control of the operator.

The unit H2 also includes a battery or other source of current I36. One terminal of this battery or other current source connects to the switch contacts I22 and I23, and the other terminal of this battery or other current source connects to the movable contact I31 of the variable resistance or impedance element I35 The free end of theresistance or impedance element I35 conditions the value of the resistance or lmpedance I35 may be controlled or varied by the operator to secure the null reading of the galvanometer or other indicating instrument presently to be described.

Another resistance or impedance element I39 is provided in this unit. One end of this resistance element is connected to the lead I38 (and therefore also to the adjacent end of the element I35 and the other end of this element I39 is connected to. a lead I40 which in turn connects to the lead I M which is connected to the free ends of both of the elements I33 and I34 The leads I40 and M! are also connected by a lead I42 to the stationary contacts I25 and I26 of the switch I I6. Accordingly the following circuit connections are established; whenever the switch contacts are moved to either the 10/1 or the /1 ratio position all of the resistance or im-' pedance elements or sections I33 I34, and I33 are connected to both of the switch stationary contacts I 25 and I26.

The free ends of the resistance ,or impedance statement of functions:

sections I33 'and 134 are connected respectively to the stationary contacts. I3I and I32 of the switch II6. Therefore, .either the resistance or impedance element I33 or I34 will be connected to the movable contact I20 of such switch, depending on the position to which the switch is thrown; and the other of said resistance or impedancelelements I33 or I 34: will be left inopen circuit condition. Thus bymoving the movable contacts ofthe switch I I6 into position to engage the stationary contacts .I22, I25, I28, and I.3I circuits will be establishedwhich include. the resistance or impedance element I33 but notftheelement I34; whereas by moving the .movablecontactsof the switch I I6 into position to engage the stationary contacts I23, I26, I29., and I32.circuits will be. established which include the resistance or impedance element I34 but not the element I33. Thus the switch IIG may be brought into position to make either the ratio element I33 or 1 the ratio element I34 effective.

The tip I03 of the plug I02 connects by a lead I43-to the'movable contact I20 of the switch I I6; and the ring contact I04 of said plug I02 connects by a lead I44 to the movablecontact H9 01 said switch II6. Likewise the tip contactI I4 of the jack II3 connects by a'lead- I45 to the movable contact IIB of'the switch 116; and the ring contact .I I of the jack II3,conne'ct by a lead-I46 to the movable contact II? of the switch H6. The lead I45 also connects by a lead I to the contact I30 of the switch H6; and the lead I46 also connects by a lead I48 to the contact I2'I of said switch I I6.

This unit II2 also is provided with a galvanometer or other null indicator I49 of relatively sensitive character so that very small differences of potential impressed across the terminals of this null indicator will cause said indicator to indicate such condition. One terminal of this null indicator is connected by a lead I50 strument is completed-through position Branch I of the' switch II of the original calculating board, returning through ring contact 61 of jack I0, cord I05, lead I46; lead I48, movable contact -I I9, and lead I44 back to the resistance-.or .-impedance element under test. It is hereto be noted that with the switch I It in the; position just described, althoughvthe galvanometer ,or

. other null indicator is connected 'tothe lead I44 to the lead I43 and also to the movable contact I20 of the switch I I6. The other terminalof this null indicator connects by a lead I5I to the lead I38 and therefore to both of the resistance or impedance elements I and I39; and to ensure protection to this null indicator against excessive potential impositions, and also to ensurefinal-and most sensitive indications by said null indicator, the following provisions have been made; a re-- sistance element I52 is placed in said lead I5I between the terminal of the null indicator and the said resistanceor impedance elements I35 and 139.; and a short-circuiting button I53is connected across this resistance -I 52 so that by pushing this button to its closed contact position the,

resistance is out out, and-final adjustments may be made with the null indicator operating under its most sensitive conditions.

The operation of this accessory unit arrangement will be understood from the following Assuming that the movable contacts of the switch H6 are in their first operating-position, the contact I20 engages the contact I30, the contact II9 engages the contact 1.21, the contact -I I8 engages the contact I24, and the contact I I? engages the contact I21. Under these conditions the resistance or impedance element of the network under'test isconnected directly to the current responsive instrument by "the following circuits; lead I43, movable contact I20, lead I41,

and lead I45,.:cord I05,p1ug' tip contact I01 to tip spring'fi8iof ,iack I0 of the original calculating board. l lrom this point the circuit to 'the inby the lead I50 no further connection-is established, sincenone'of theyswitch contacts I22, I23, I25,-I26, I28, I29, I3 I or, I32 is engaged by a movable contact of said switch. Under these conditions the current responsive instrument 43 I will be caused-t0 indicate current flowing in-the resistance ror'impedance under test it (or inversely, the resistance or impedance of said-element) by a ratio of 1/1 'or unity. This is the condition .Whichis equivalent inall respects to the-normal conditions of -operatiorr "of a calculating board such as disclosed inyrny said .p'atent,.No.l2,30l,4'Z0, when no *such accessory as here :described :is available or connected into the circuit. I I

:In Figure 2 I have shown schematically the foregoing connections which exist for this first or unity ratio conclition. I

Next, by moving the switch contacts I20, I I9, I I8, and II! to the next or second operating position, :the' contact I20 engages the contact I 31, the contact I I9 engages thecontact I28, the contact -I-I 8' engages the contact I25,and the contact I'I-I engages the contact I22. 'With these connections established we fined the following circuits to be effective; the current flowing through the resistance or impedance element under test flows through the element I33 in full volume to the'point 'ofzjunction of the leads I40 and I 42 which latterconnects to the lead I45 through ithe'movablecontact I I8). There is also established, withthis switch position, a further and local'circuit whichincludes the resistance orimpedance element-"I38, and'the resistance or impedance element, I35 'withthe battery I36. The lead 'I45-leads to oneterm'inal ofthe current responsive instrument, and the other terminal of this instrument connects by'thelead 1146 'to this local circuit. The battery is so connected that its eiTect is to cause a now of current through the resistance or impedance elements I35 and 139 in direction'opposite tocthe flow of current firo'mithe'*Sn'etwork element under test (which current comesiin roverthelead 1'43 and through the "resistance or impedance element I33). Consequently *ther total current flowing throughthe current responsive instrument 43 is .the sum of both the current flowing throu h the networkeleme'ntunder test and this locally or battery'induced' current, that is, the actual currentfio'w'ing through the current'responsive instrument isincreas'ed over the current actually flowing'through the-network element.

The junction "point of the two resistance or impedance elements I35 and I39 is connected 'to the other terminal of the network element undertestbythe lead 'I 4'4'1(coming over the lead positioning of the movable switch contacts into this second operating position the null detector or indicator I49 is also connected between the two leads I43 and I44 of the system so that any difference of potential existing between these two leads will be at once indicated by a deflection of the needle of such null indicator. Contrarily, when said needle shows no deflection it will be known that both of the leads I43 and I44 are at the same potential, notwithstanding that the current flowing through the network element under test is being passed through the accessorv unit now under consideration. In other words, there is actually no drop of potential occurrin through this unit and its elements and connected parts, as far as the outside effect is or may be concerned.

In Figure 3 I have shown schematically the foregoing connections which exist for this second or /1 ratio condition. Reference should therefore now be made to this Figure 3 for a sim le illustration of the circuits thus established.

In F ure 3 the resistance or im edance element I33 for the ratio 10/1 is of fixed value (once it has been calibrated). The resistance or impedance element I39 is also of fixed value. When the network element is connected into the circuit bv plugging into its jack 2! a current will flow throu h the resistance or im edance element I33 producing a dron of potential throu h this elem nt. However, the battery I35 will produce a current flo c ming to the junction point of lea s I49 and I45. and there oin ng the current arriving from the network element under test. The total current so produced will then flow through the current responsive instrument 43, sub ecting that instrument to an exaggerated current value and correspondingly causing an incr ased deflection of that instrument to occur, such increase de endin on the value of this superimposed current. This superimposed cur rent will also flow through the resistance or impedance element I39 causing a drop of potential to occur over such element; and due to the fact that the potential drops over the two elements I33 and I39 are of opoosing si n it follows that the total potential difference between the leads I43 and I44 will be the algebraic sum of these drops across the elements I33 and I39; and the I indicator I49 will thus be subiected to this algebraic sum of potential differences. Such algebraic sum may be in either direction, or may be zero, in which latter case said null indicator I49 will show no deflection; a-null indication will be iven.

When the network element is first introduced into the circuits as just explained this indicator I49 will almost always show a deflection in one direction or the other. Then, by adjusting the variable resistance or impedance element I 35 the current flowing through the branch circuit may be either increased or decreased until the potential drop across the resistance or impedance element I 39 becomes e ual to the drop across the element I33. Since these two drops are in opposition to each other the net drop between the points of connection of the leads I43 and I44 will become zero under the conditions just above stated. The null indicator I49 will then show a zero deflection. Thereupon the current responsive instrument 43 may be read, and its reading will be under'the condition that no loss of potential is occurlng between the points of connection of the leads I43 and I44. This is equivalent to securing the reading of the instrument under the condition that the equivalent resistance or impedance between the connections I43 and I44 is zero, corresponding to a zero resistance or impedance of the current responsive instrument and the connections, immediately related to it.

Under this condition of a null reading of the null indicator the drops across the elements I33 and I39 are equal to each other. Since the current flowing through the instrument 43 is equal to the sum of the currents flowing through the elements I33 and I33 it follows that a definite relationship is established between the magnitude of the current arriving over the lead I43 (and departing over the lead I44), and the magnitude of the current flowing over the lead I45 to the instrument 43 and arriving from said instrument'over the lead I46, under the condition'of a null reading of the indicator I49. In other words, a definite ratio is established between the value of the current being measured by the instrument 43 and the true value of the current flowing through the network element under test. That ratio is determined as follows:

Let i designate the current value flowing through the network element (arriving over the lead I43 and departing over the lead I44); let I designate the current value flowing through the element I39; let T designate the resistance or impedance of the element I33; and let R designate theresistance or impedance of the element I39. Then,

i r=I R for the null condition. Now let I1 designate the current value flowing through the instrument 43 (flowing out over the lead I45 and back over the lead I46). Then,

I1=t+I also, 7

I =i r/R Upon substituting we get,

and finally,

In other words, the ratio of the current flowing through the current responsive instrument 43 as compared to the current flowing through the network element under test is equal to unity plus the ratio of the impedance of the element I33 divided by the impedance of the element I39. This equation therefore provides us with a simple means to determine the relative values of these impedances I 33 and I 39 for any desired multiplication of the true value of the current flowing through the network element to determine the value of the current flowing through the instrument 43 for the null condition. In other words, by this equation we may determine the relative values of the impedances of the elements I33 and I39 for any desired multiplication of the and oi sufficient impedance range't'o enable not onlythecarryin of the needed current, but also to enable'control of the volume of that current with accurate adjustments by means of the :adjustable section I35 to enable bringing the circuit tothe balanced condition as shown by the null reading of the instrument I 49. -As -a simple illustration of actual ohmic values of 'th'e-elementsliifi, I33 and IN the following illustration is given:

By assuming a value of 70 ohms for the ele ment- I39, and a value of 630 ohms for the ele "ment I33, we find that the ratio Ii/i becomes equalto '1 plus 630/70, or 1 plus 9, or 10. Like- "w'ise,by"-leaving the element I39 at'lO ohms, and *selecting an ohmic value'of '6930for the element I-34,-'we find that the ratio Ii/i becomes equal to 1 plus'6930/70, or 1 plus-99, or 100. Therefore by selecting the value of 70 ohms for the element 139, and the values of 630 ohms and 6930 ohms for the elements I33 and I34, respectively, it is possible to obtain ratios of lo'and 100 by moving the switch IIB to its second and third positions, respectively. Evidently, if desired a greater numberof switch positions might be provided, of additional ratio values, or other combinations of ratio values and numbers of switch positions could be provided for optionally.

Conveniently'when using the features of the present invention in an accessory for use with a 'calculatingboard of the type of my earlier patent, No, 2,301,470, the various elements of such accessory as shown in Figure 1 may be incorporated within a'box or housing of relatively small size and weight. The top of this instrument may 'be'of-an insulating'p'anel, thesame carrying the switch element-I I6, null'indicator I49, and a button or handle for adjustment of the resistance "or'imped'ance section I35 in order to adjust for the null reading-condition. The switch IIB may be provided with a single control button whereby the several movable contacts III, II8, H9, and 120 maybe brought simultaneously to'either of positions 1, 2 or 3. Thepanel board may then be provided with suitable markings to indicate the momentary position of such adjustable button. This panelboard or box topmay also be provided with the jack element H3; and the accessory end of the cord I! maybe connected into the accessory inconvenient manner. Within this accessory box may be contained the-several re- 'sistance orimpedance elements I33 I33 I34, I34", I52, I39. I35 I35 and the battery I36 *may also be contained within this box-like accessor-y. With this convenient arrangement of the accessory unit'it becomes possible to use the present improvements in connection with previouslybuilt calculating boards embodyin-gtthe fea-- tures of my earlier patent, and Without the need of 'any changes in such earlier calculating boards construction. Such an-accessory unit as'just described may be brought into a size of substantially 7" long, 4 wide, and 4" high for use with a calculating board having any numberof network element simulating elements.

, 14 It is notedthattheresistance oriimpedanc'e 135 is conveniently divided into'twosections' I and 135 for the-following reasons: The local battery 436 is conveniently of about 4- /2 volts potential.

I By dividin the element I35 into two sections,

'I35sand- I 35 and by making'the section I135 of, say-I ohms impedance, there willalways beian impedance of at least 2 20 ohms in the circuit of the instruments?) (150 ohmsin the section .135

an'd' 'm ohms in the element I39, disregarding the impedance of the instrument 43 itself). Thus adjusted to any position other than zero the current flowing through theinstrument 43 will be correspondingly reduced.

I have now disclosed in detail a convenient form-of "an accessory unit intended for use with previously built calculatingboards of type embodying the features of said-earlier patent, No.

2,301,470, to-enable use of the improvements of the present invention with such previously built calculatingboards'I shall now'disclose an embodiment whereby the improvements of the present In aconvenient embodiment of the accessory v unit the rheostat I35 is made continuously variable between zero and at least'15.000 ohms. Preferably also this rheostat is of tapered ohmic values: so that'therate ofchange of resistance or impedance per degreeof rotation of the control button is small at small values of impedance, and islargerat larger values, to facilitate smooth and accurate adjustment.

branches. by-thepractical consideration that-complete beneselected settings. mi-ts full use of the entire available impedance invention may be incorporated into calculating boards yettobe built.

lnthe above describedaccessory unit the benefits of the present improvements aresappliedonly in the measurement of current in the'network This limited application is dictated fits are obtainable only by extensive revision of existing wiring of the original calculating board. In the application oi? the present "invention to completely new calculating boards, the benefits of zero equivalent impedance of the current measuring instrument are made available also in the adjustment of individual impedance elements to It will be seen that this perrange of these'elem'ents without introducing any errordue to insertion impe'danceof themeasuring instrument. When the features of the present invention are-to be incoporated'intonew calculating boards the wiring maybe originallydesigned to not only incorporate said features di- 'rectly in such calculating boards without the necessity of providing-an accessory'unit-such as already described herein. In so doing it is also possible to incorporate in such revised wiring of the newcalculatingboards certain additional features which I shallmenti'on at this point.

In said earlier Patent No. 2,301,470, provision ismade for variation of theresistancelG disclosed in that patent-from time to'time so that compensation 'could be-made for changes-iii battery'voltage or other supplied potential, and likewise, in

crderthatthevoltmeter 51 shown in that-patent may be'so adjusted'that it will correctly'read the per unittvoltage, there'is provided the resistance 54 in that patent. The resistances 46 and 54 of that patentshouldbe adjusted to the correct value corresponding to the battery terminal voltage then present. Itis, however, to'be noted that such an adjustment, while providing for change of battery voltage with age or other causes, did not multiplications of errors dueto slight changes of voltage are introduced, so that when using the improvements of the present invention which have already been disclosed it is also desirable to hold the voltage delivered to the network more closely to a prescribed value, for example, 18, regardless of the value of the battery voltage (or other source), and regardless of what the value of the current load on that battery may be. I have, therefore, incorporated in my present improvements when used in newly to be built calculating boards, special means to compensate for any slight changes in voltage, whether due to changes of battery loading or otherwise, during the conducting of the various tests to be conducted on the calculating board. These provisions I shall presently disclose herein.

In the circuit arrangements illustrated in said earlier patent there is provided a reversing switch whereby the polarity of the current responsive instrument may be reversed if necessary to ensure correct reading of such instrument when it is used for various tests. When the improvements of the present invention are incorporated into a newly to be built calculating board it is necessary that the currents flowing through the two resistances or impedances I33 and I39 (see Figures 1, 3 and 4) be through both of these elements towards the common connection I45 .(or from said connection) in order that the desired balancing of potentials may be secured to enable a null indication to be given by the instrument I49. In order to secure this result as well as to ensure proper functioning of the current responsive instrument 43 I have included in the modified circuits of such newly to be built calculating boards a reversing switch whereby the polarity of the bus-bars 31 and 33 of the network element under test or adjustment may be reversed, thus ensuring correct operations in all circuits.

A further improvement in the circuits of such newly to be built calculating boards embodying the features of the present invention as well as the features of said earlier patent is as follows:

In that earlier patent I illustrated a five position switch '11 to enable the securing of the various switching combinations required as shown in that patent. Since in newly to be built calculating boards embodying all of the features which have been disclosed herein it is necessary to make provision for reading in three ratios (l/l, 10/1, and 100/1), the incorporation in that switch all of the functions assigned to such switch in said earlier patent, plus provision for two additional switch positions needed to enable functioning of all three of such ratios, it would be necessary to provide for seven positions in that switch. Furthermore, with such an arrangement it would be necessary to pass through the positions of 10/1 ratio and 100/1 ratio in order to reach the position of Read Total I (such as shown in said earlier patent). Such an arrangement would be undesirable for various reasons, including possible trouble by overloading when moving to this Read Total I position. Accordingly, I have, in the circuit arrangement presently to be disclosed for such newly to be built calculating boards provided a special jack for such Total I readings, into which special jack th plug 69 of that earlier patent may be inserted. Thereupon the switch may be moved to any one the three ratio positions to measure the total current by use of the selected ratio as determined by such switch position.

I shall now describe an arrangement of calculating board which includes the features of that earlier patent as well as the features of the present invention, when all of said features are embodied in a newly to be built calculating board. For this purpose reference is now made to Figure 5.

In Figure 5 I have shown the current responsive instrument 43, the voltmeter 5|, the battery 95, the resistances 64 and 54 for the voltmeter, the jack 69, and the reversing switch I98 corresponding to like elements of said earlier patent. I have also shown the busbars 31 and 38 of one of the network elements shown in that earlier patent, and it will be understood that other network elements may be incorporated in these newly to be built calculating boards, and that the one shown in Figure 5 is merely illustrative. In Figure 5 I have also shown the switch 1| corresponding to the like numbered switch of that earlier patent, but in the present case the switch illustrated is provided with six live positions instead of five as in that patent.

The switch 1| of Figure 5 is provided with the five movable contacts I54, I55, I56, I51 and I58 which are conveniently connected together so.

that they will move in unison. This switch is provided with six live positions to either of which positions the movable contacts may be adjusted. Thus, there are the stationary contacts I59, I60, |6|, I62, I65 and |64 for the movable contact I54; there are the stationary contacts I65, I66. I61, I68, I69 and I10 for the movable contact I55; there are the stationary contacts |1|, I12, I13, I14, I15 and I16 for the movable contact I56; there are the stationary contacts I11, I18, I19, I89, |8| and I82 for the movable contact I51; and there are the stationary contacts I83, I94, I95, I86, I81 and I88 for the movable contact I58.

The movable contact I54 is connected to the positive terminal of the battery by the lead I89; the movable contact I55 is connected to the negative terminal of the battery I36 by the lead I99; the movable contact I56 is connected to the tip contact 68 by the lead I9I; the movable contact I51 is connected to one terminal of the null indicator I49 by the lead I92; and the movable contact I58 is connected to one terminal of the voltmeter 5| by the lead I93.

The multiplier rheostat 54 is provided, together with the fixed resistance 64, both for the voltmeter 5| and corresponding to like parts of the circuit shown in said earlier patent. The resistance 64 is connected to the free terminal of the voltmeter 5| by the lead I94, the two rheostats are connected together, and the slide or adjustment contact |9,5 of the rheostat 54 connects to the lead I96. This lead connects through the fuse I91, and by a lead I98, to the negative terminal of the battery 95. The slide contact I95 enables adjustment of the total resistance in the voltmeter circuit between limits determined by the resistance 64 and 64 plus 54. The total resistance is factory adjusted to a value such that a preselected voltage, say 18 volts, will produce a, deflection of the instrument 5| corresponding to 1.0 per unit voltage, and

A short-circuiting but- The resistance element 135 (including the av sections I and I35 is connected between the lead I92 and the positive terminal of the battery I36. The section I35 .is adjustable in manner similar to "the like section shown in Figures 1, '3 and 4. The fixed resistance or impedance element I39 is connected between the lead I92 and one terminal of the current respons'ive-instrw ment -43 to which terminal this element I39.is connected by the lead 203. This lead .203 (and the corresponding terminal of theinstrument 43) is connected to a lead 204. To this lead 204 there are connected the adjustment'slides 1205, 28612.net 201 forthe adjustable sections dils I33 rand I34; respectively; Thesesections I 33 and I3 correspond to the sections of like numbering shown'inFigure 1; being for the 10/1 and 100/1 ratios respectively. The additionalsection 203 introduced into Figure. 5 is for the 1/1:ratio, and will be discussed further. hereinafter. Corresponding to these'adjustable sections .208 I33 an' ;1.*I3l are the fixed sections 208 Iii-8 and 134 the sections I33 and II 3'4 'correspondingto like inumbered sections shown in Figure '1. It isinten'ded thatthe'sections'zilil 133?, and 536'" shall be brought to exact adjustment and sealed at the factory; thus said sections constitute fixed factory adjustments. f

:The free terminals of the threetsections 2.08, I 33, and I34 are connected to the fixed-com tacts 1214, I'Iiand I13, respectively, ofthe switch element TI; .50 that the movable contact I56 of s'aidswitch will progressively engagethese ,fixed contacts and thus'progressively be connected to the three-sections 2138; I33 and I34 for the three ratios 1/ 1, '10/1,'and 100/1. 'It :is also noted at this'point th'at the two additional fixed contacts I12 and I'll which maybe engaged by this movable contact I56 are connected to the fixedcontact I'M by the lead 209. Therefore the l/l ratio element 208 is ensured for either of the three switch positions III, I12, or I14; and the intermediate switch position, corresponding to the fixed contacts IBI, I57, I13, I19 and I85 is the off position all ofrsaid stationary or fixed contacts being dead.

The free terminal .of the current responsive instrument 43 is connected by the lead 210 to the stationary contacts I10, I69, I68, I86 and I corresponding to the movable contact I55 of the switch H Thus the instrument 43 is com nected'to'the movable contact I55 (and thus to .thelead I190) for any of the-five operating positions of the switch I I.

As a means of adjusting the voltage delivered to the calculating board load without regard to The opposite end of the rheostat element 2 I2 .is connected to the lead 198 by means of thelead 215, a fixed 'resistance 2 I6 being introduced into this lead 2I 5 as shown. The slide 213 is connected to the lead I93 by a lead 2I'I. With this arrangement it will be seen that the following functions are introduced into the system:

:Since the lead I93 connects to the movable contact I58 of the switch -'I-I=* itfollows that whenever said switchis moved to any of its operating posit-ions (other than off) this lead i-sconnected to one of the stationary contacts I98, I81, I86, 184 or I83 '(the'con-tact I 85 being the off Contact). The slide 213 is therefore brought into "contact with these stationary contacts forvarious switch positions. Now it will be seen that movement of the slide 2I3 towards the left will increase the amount of the resistance elementiZII between the positive terminal of .the batteryxand the lead I93 (and therefore also between the positive battery terminal andrthe movable contact I58 of the switch H y. This movable contact is the one which connects to :the network element or to the portion under test, soby movement .of this slide the amount of thelresistance 2II introduced-into this portion of. the circuit may be adjusted. At the same time since this lead I93 connects toone terminal ofthe voltmeter-5| it follows that by :adjustment of the slide 2I3 until a desired voltmeter reading is indicated there :will be :assurance that the element or elements connected to the switch contact IE8 is or are atthe same potential as the terminal of the voltmeter-to which the-lead :I93 is connected. Thus. if due to increased loadingof the network an. increased demand for current is produced, thereby increasing-the battery .load and increasing the internal drop inthe battery, the slide 2-13 may be moved slightly to the right, thus-cutting out some of .the resistance element 2.I I contained in the circuit, and correspondingly raising the potential of the end of the network which is in connection with the slide. By this means the effects of internal battery drop may be'neutralized, and the potential impressed on the network during test may. be maintained constant.

:Now it is. noted that movement/of the slide to the left increases the'amount of the resistanceelement .-2I I in series with the networkelements, but at thesame time such leftward movementof the slide decreases the amount of the resistance element v2H2 contained between the slide .and'the negative terminal of the battery. It'is also, noted that between the two terminals of fthe battery 95 there must be absorbed the full battery voltage through the following local circuit; lead I89, movable switch contact I54, lead 2M, that portion of the resistance element ZII lying to the right of the slide 72I3, that portion of the resistance element 2'I2 lying to the left of the slide 2I3, lead 2I5, resistance element 2 I16, and lead I98. Now as an example, the total resistance element 2| I may be of the order of 645 ohmsgand the total resistance element 2I2 may be of the order of "10,000 ohms. A given linear displacement of the slide'therefore results in change of the amount of resistance of the element II I .in series with the-load, but also results in a change in the amount of theresistance 2I2 in parallel with the load. Furthermore, in case of extreme movements of the slide towards the left,'with corresponding large reduction in the amount of the resistance element 2| 2 in parallel with .the load, the resistance-element 2| 6 will 19 always be present to prevent any excessive flow of current. Thus adequate current flow through the element 2I I is obtained at all times to assure sufficient drop thereacross to obtain a desired delivered voltage, no matter how small the network current may be.

The tip contact 68 of the jack 65 connects to the movable contact I56 of the switch H the ring contact 61 of said jack 65'connects by a lead 2IIeto the stationary contacts I80, IBI and.l82 of the switch'll and'the sleeve contact 66 f said jack 65 connects by' a lead 2"! to the stationary contact I83 of the switch H and also to one end ofthe calibrating resistance element '46 which resistance corresponds to the" resistance element-oflike numbering in said earlier patent. The other end of said resistance element 46 connects to the stationarycontact I84 of the switch Il Accordingly,-when the movable switch member is moved'to its lowermost position the contact I58 (and therefore the lead I93) is connected directly to the sleeve contact 66, whereas when the movable switch member is moved to its next higher position the resistance element-4 6 is introduced into'this circuit. Since the voltage corresponding to 1.0 per unit volt is nowfactory pre-set in quantity, the resistance of the element 46 may now also'be factory preset 'and sealed, reducing the number of adjustments required of the operator. I

I; have mentioned the provision of a special jack inthe present embodiment of the features of the present invention in newly to be built calculating boards,- such jack'being designated as Total I. This jack is shown in Figure at 2l 9. It has the tip contact 220 which connects to the lead 22 I; and it has the ring contact 222 which normally connects to the tip contact220 by means of the spring contact 223; and this ring contact 222 connects by the lead 224 to the stationary contacts'lfl'l and I18 of the switch H A lead-225 connects the lead 224 to the lead I96 already referred to.-

V It will also be seen that with this embodiment of the features of the present invention incorporated into newly to be built calculating boards, when the plug of the cord is inserted into the jack 2I9 and the switch is moved to its second position (first below the off position) the Z plusnl position is dead due to the fact that the sleeve contact of the jack'2I9 is open and this is also true of the arrangementwhen the switch is moved to its first position (second below the off positiomi However, with the plug inserted into this jack 2I9 the total current may be read on the basis of either of three ratios, by then moving the switch to either of its fourth, fifth or sixth positions (first, second and third above the foif position), as will be apparent from study of the circuits of Figure 5.

' I have already referred to the reversing switch I08 of said earlier-patent, and to the fact that in the presently being described embodiment this switch has been set to a location in the'circuits different from its original location in the circuits 'so that it may be used for directly reversing the bus-bars 31 and 33 of the network element. The central leaves I09 and I I0 of this reversing switch are connected directly to the bus-bars by the leads 226 and 221 respectively. The two outside contacts I l I and H4 of this reversingswitch are connected together by the lead 228, and this lead 228 is itself connected by the lead 229 to the three stationarycontacts I86, I81 and I88 'or-the switch 111 -The two inside contacts 1 u and II 3 of this'reversing switch I08 are connected together by the lead 230, and this lead is itself connected to the lead 22I already referred to. 1

It is understood that the jack or the jack 2I9 is intended to receive one of the end plugs 69 of the cord 29 shown in the calculating board arrangement of that earlier patent, No. 2,301,470, with the plug of the other end of such cord inserted into that jack I3 corresponding to' a selected network element to be adjusted or tested. Upon inserting the end plugs of such cord into the jack I3 of the selected network element and the jack 65, respectively (of the arrangement shown in Figure 5 hereof it will be found that the circuits shown schem'a'ticallyin Figures 2, 3 and 4 will be simulated, and that by moving the movable switch member upwardly successively to its fourth, fifth and'sixth positions (first, second and third above the off position), the circuits incorporationg the features of the present invention will successively be reproduced with the resistance elements 208,. I33 and I34 successively introduced into the circuits so established. Suitable values of these constants may be selected according to the requirements of the calculating board, and the desires of the designer, but for the case of ratios of 1/1, 10/1, and 100/1, the following values have been found satisfactory:

There being three of the resistance or impedance elements 1' in connection with the switching means, these elements may be suitably proportioned for the 11/1 ratios of 2.0, 20.0, and 200.0, respectively, according to the principles already explained herein. Then it will be evident that the true current ratios flowing through the current responsive instrument 43 as compared to the current actually flowing through the network element under test will be 2.0, 20.0, and-200.0, respectively. However, the face of the instrument 43 may be marked with scale readings showing true values of current flowing through the network element, or true values of Z of said network element or said scale may be provided with ratio markings which will inform theoperator of the basis of the ratios being currently used. The following constants are mentioned as giving the ratios above mentioned for 11/1:

True Marked ratio ratio T R 2/1 1/1 70 70 20/1 10/1 1, 330 70 200/1 Noll 13, 930 70 Based on a voltage of battery 136, of 4%. 7

It will now be seen that when the features of the present invention are incorporated into newly to be built calculating boards it is possible to obtain not only these features which have been disclosed-in connection with the accessory unit arrangement, but also additional features now;

" variations in power supply voltage.

amplifiers must introduce practically zero phase shift So they are expensive andrequire hi'ghly am-s ssy;

, 21 sitive thanrdirect chrrentinstrumcnis :of: :equiva lent "range, introduce :lnto the circuits. of

which they comprise portions a". substantially greater impedanoe than is :inserted by direct current. responsive instruments :inserted v:into such circuits. For this reasoniit .hasheretofore been.

found.n ecessaryrinzthecase of'rcalculatinggboards intended. for. operation on alternating "current sourcescto :use one of two :methods to' avoid serious errorsdue to such :high impedance values of the-alternating ourrentrinstruments themselves. These methods haveheen as follows: @AQThe use of relatively large currents! and voltages in :the calculating hoards.

levels so that the powerz1disslpated in'lthe instruxment itself .is not 'a' seriously large-portion of the f totalr This practice has demanded the :use .of

elementscapable-zof zc'arrying large currents without .over' heating and is -ifurthcrmor'e inherently costly, both in 'lconstruction oi: the calculating board;and.its operation. I

-B. :The use of"electronicamplifiers between the circuit to be metered andathe instrumentsiusedin metering it. Such amplifiers must be exception--.-

ally stable in gain over was periods of time, over wide ranges of measured quantities, and over Also these skilled periodidms'pection and .maintenance.

'-When using thefeatures of the present inven-' tionin calculating boards intended for operationon' alternating current sources use can bemade ofcommeroiallystandard alternating current 1in- .strument movements, =zero impedance is. introducedinto the circuit which includes the network element under test, and-it Ebecomes possible-forthedesigner of the :calculating'hoardto' 'seleot current :and voltage levels for such calculating board which the designer mayfind most favor able-without subordinating them to c'onsiderations imposed by the characteristics of the instrument itself.

Additionally it isdesirabl'e that the operator be able to measure the flowof powenboth real and I reactive, "and withdue regard 130 51811, .a require ment which maybe met. -'by-:a1ternating current operated calculating boards embodying the features of the preesntinven on-as will presently ber seen.

.Measurements :of impedanceiinoluding bfithill'e sistance and reactance; when-using alternating current sources, necessarily include provision for indicating amount and direction of -phase disr itself. It iS'LELISO necessary that the operatorbe able to determine not only the magnitude of tour,

rents andivoltages, :but the'phas'e'position of: these quantities as we'll.

.Re'ferencemayfnow be had to Figure 6 which shows a" typical circuit 'for. making possible the .This 118. equivalent to employing sufiiciently large power application of the features of the'presentinvent'ion Lto a" calculating hoard embodying :ith'e in-.

vention not said carlierlpatent; No. 2,301,471), to gether with the features. of :the present invention whcn using "alternating current source of cur-. renniand when. the elements-of thenetwork under: test incorporate thepresenceof reactancesaas wellrasiresistances.

Figure 6. I have'ishownxa single network .ele-

ment, ;23 1- corresponding to one of the network elements of the showin sillustrated in said earlier:

patent;'No. 2;301,470 ibut atheelement 23.! is provided with. two sections 232 rand'233, theformer of which is' substantially purely resistive and the latterof which is :substantiallypurely reactive in character.- Eachof these elements is adjustable in. amount, the movable contacts 234 and 235' making provision forlsuch adjustments in values of: resistance andreactance, respectively. These sections 232 and 233 maybe placed in seriesconnection' by the jack contacts 236 and 231, so that normally'the'two sections arein serie connection between the element terminals 238 and .239: Thus it ispossible to adjust the complete network element- 231 to any desired condition of'resistance and'reactance to simulate a real network-element of the-network being simulated. -"Ihe jacks 240 and 241 (having the tip rcontacts 236* and 23-1 alreadymentioned) also have the.

ringcon'tacts 242 and 243 and'thetsleevecontacts 244 and 245,-respectively. The sleeve contact 244 connects to the'termina'l 238 and therefore toone end of the resistance section- 232; the 'ring'contact 242 of the .jack 240 and the sleeve contact 2-45 of-the jack 24l .bothconnect tothe reactance' section-233; theringucontact 24.3 of the jack 24l:

; connects to the termina1'239; and the tipcontaot 23105 the jack 24.1 also connect to'the adjustable contact 2350f the 'reaotance section.

= A-suitable'cord is provided having the three leads 245, 241 and 248- which are connected to the three o'ontactsof the plug 249 which is'provided at the iree end of this cord. Upon inserting this plug 249 into the jack 240 the lead 24'! is placed'in connection with the terminal 238, the lead248 isplaced in connection with the reactance section 233 and thelead249 isplaced in connection with' the adjustable contact 234 of the 'resistance'sec tion- "At the same time the engagement "ofthe tip contact of the'plug with thecontact236 serves to open the circuit previously existing directly between the-adjustable contact 234 o'fthe resistance section-and the reactance' section, and serves to insert the leads 248 and 249 into the circuit between these sections. With the plug inserted into the jack L249 Lit'is therefore possible to read or determinethe resistance of the resistance'sec tion by use o'f theleadsil'fl and 249; andit is also possible-to measuretotal current flow'throughthe resistance and reactance sections in series. Upon inserting the plug-into the jack 24! the lead- 247 isplac'ediinconnection with the reactance section.

23'3-and with the movable contact 234 of the resistancesectiomthelead 248 is plac'ed in connedtionvwith the terminal .239, and the lead 2431s placed inconhection with the adjustable contact 233 of the reactance section. At the same time the engagement of thettip contact of the plugwithi the: contact 12311 serves to open the circuit prev iously. existing between the "adjustable contactofj the reaotance section and the terminal 239, and

serves 'toir-isert 'theleads 248 and 249 into the circuit between these elements. With the plug inserted into the jack 24! it is therefore possible to read or determine the reaotance otthere actance section by use of the leads 24.1 and. 249;:

audit is also possible :to measure total current.

23 flow through. the. resistance-and reactance 'sections in series. Evidently thereforeI have made provision for individual adjustment of the magni-- tudesof resistance and reactance of the sections comprising this network element (or any other such network element); I have made provision for normally placing these sections in series connections between the terminalsgof such network element; and I have also made provision whereby each' of said sectionsmay be brought into connection with some other instrument by leads of the cord inserted into the jackcorresponding to such network element section, thus making it possible to adjust'the resistance and reactance .sections individually to the desired values of resistance and reactance to simulate the real-network element. I shall now show how such adjustments of ythe resistanceand reactance sections may be measured by means incorporating the features-of invention already disclosed herein respecting the adjustment of simple. resistance elements.

I have described one method which employs the structure disclosed in Figure 6 and by which it is conv nient to separately adjust the. resistance and the reactance of the respective sections of the net work element 23 I. It willbe understood that any one of several circuit arrangements may be used to accomplish such an adjustment, the preference being influenced by design considerations. For example, if the circuit constants selected are such that the resistance inherent in-the inductor 233 of Figure 6 is too large to be neglected, the circuit arrangement shown in Figure 9 may be substituted for that portion ofFigure 6 WhiCh'COIH".

prises the network element 23 I. I In Figure 9'c0nnections of the inductive reactance section 233 and the jack 326 which is associated therewith are substantially unchanged from those shown in Figure 6, and the adjustment of this reactance section is accomplished by the insertion of the plug 249 into vthe jack 326 as previously described.- The'connections of the jack 32! provided for the adjustment of the resistance section have, however, been altered by connection of the sleeve 328 to include in the circuit between the sleeveand tip contacts both the reactance section,

233-and the resistance section 232. If a source of directcurrent is employed in the adjustment of the resistance section, the current will pass through both the resistance andreactance sections in series and a direct current responsive instrument, provided with a suitable scale calibrated in impedance terms, may be caused to indicate theresistance of the complete network element as described in my aforesaid issued patent, No. 2,301,470. Such a direct current will not, except-for transients of short duration, be affected by the reactance of the complete network section. If the resistance of the reactive section 233 is negligibly small as it may be when certain design constants are used, the circuit connections of Figure 6 provide adequate accuracy; with other values of design circuit constants the resistance of the reactive section may be suflicient tov require the use of the circuit connections shown by Figure 9 to obtain acceptable overall accuracy. Other possible circuit connections differing in detail from either Figure 6 or Figure 9 may be found to afford advantages in specific cases. For example, when a network element is employed to represent a load in a real network, it' is convenient to adjust not the resistance and reactance of the element as such, but to adjust the in phase and the quadrature components of the current flowing-through the load. Such adjustment is facilitated if the resistive and reactive sections of the.

lelinsteadof in series as shown in Figures 6 and 9. Parallel connection is advantageous in this condition as it permits separate measurement ofthe resistive and reactive components of the cur rent and independent adjustment of either. Accordingly, I do not wish to be limited to the detail connections shown for a network element'except as I may limit myself in the claims to follow.

Each of the sections 232 and 233 could be brought into correct adjustment, the one for value .of resistance, and the other for valueof reactance, by impressing a 1.0 per unit alternating voltage across these elements, one at a time, and observing the deflection of a suitable current responsive instrument in series circuit therewith, this'being facilitated if the instrument is provided with an appropriate scale calibrated in per unitI impedance, and further provided that the impedance of such instrument were sufficiently low in comparison-with the impedance of the network element being adjusted. If any impedance be present in such instrument the ac- Y curacy of the adjustments will be impaired acsections of the network element use may be made, of means according to the principles already disa closed herein; but it must now be, noted that should an alternating current be passed through the scheme as shown diagrammatically in either.

.' of Figures 1, 3, 4 or 5, flowing between the leads. I43 and I44 of Figures 1-,- 3 and 4,;or between the leads I82 and 20! of Figure .5, the currents. momentarily existing in the branches I33-and- I39 (or corresponding thereto), and-in the elements of such branches, would generally be-out of phase. Generally the phases of the currents flowing through these impedance'elements would. be diiferent, and the amount of such difference would depend on many factors including the further effect of the impedance of the current responsive instrument itself. And since these cur-. rentswould also: differ in magnitude, and since such difierence in magnitude would also depend on variations of the adjustments of the impedance section I35b,'the effect of such phase differences would be reflected in varying man-. ners on the indication of the null indicator. For these and other reasons it is necessary to make special provisions in'the'circuits, and to provide a special form of null indicator in place of the simple form of instrument. I49 which is usable when direct current sources'are provided insteadof alternating current sources. I shallnow disclose the further provisions which I have made to enable the successful application and use of mypresent invention in the caseof alternating current sources of supply. and operation.

I provide a source of alternating current 250. A preferred form of this source, and one which is well known in the art, comprises a polyphase winding, 25I in a suitable stator frame. This stator element provides a rotating field when supplied with polyphase currents by impression of polyphase voltages to the phase windings of this stator element. The rotor element/252 10- cated within this stator is provided with a single phase winding; and by blocking this rotorelement at a proper phase position with respect to. the stator element the single phase voltage in-. duced. in this rotor winding will bear a specified 25 or' 'desired phase position with respectzto the voltages impressed on the stator winding; This rotor may be readily blocked or.held stationary at adjusted phase position in simple manner, as byprovision of a hand wheel adjustment. pro vided with degree markings by which the angular position of suchadjustment may be known, and by provision of suitable. means to'lockv the hand wheel. in such adjusted position. Such means are well known.

The vso-provided and phase. controlled single phase voltage is: used to excite. the primary 2.53 of a transformer 254 and the. secondary 255- of this transformer may be tapped as shown at 256 so that. the switch 251 may be moved. to proper position. to deliver the desiredvoltage to the'leads 258 and 259. A. voltage of controlledjmagnitude and controlled phase position is thus madeavailable for the calculating board now: being described.

There is provided asource of. alternating cur.- rent voltage; in synchronism with the source 258-459., and of fixed phase. position, with which the source 25.8-259 maybe compared. For this purpose I have illustratedlthev transformer 2169 having its primary 26! connected to one leg of the polyphase source 250 as shown: inFigurefi, by the. leads 262; and 2.63,. a. cutout switch 264 being provided in these leads. Thesecondary 295 ofrthis; transformer may be. tapped as. shown so ously herein. However; whenusingalternating current sources of: supply itr'will generally be desirable to provide an additional ratio for the. idl lowing'reason: I p .1

' The usual commercialv movements of alter.- nating current instruments are readable. only fromabout. 20% ,of. full scalepto full scale... It is therefore desirable to provide agree-terrange of ratios when. using; alternatingcurrent sources than when using direct current sources; and'fior this reason Iv havain the arrangement-now tobe described nade provision for four ratio positions.

.In Figure 6 thereis shown the switch unit 210.. This; is provided with the; three movable contacts 21!, 212 and 213. Corresponding; to the movable contact 21! there aretheeightstationary contacts 214, 215, 216,211,, 218, 219;, 28.0 and 28!; corresponding to the-movable. contact 212 there; are, the'eight stationary contacts 282, 283,. 284,285, 286,, 281, 288 and 289;, and corre sponding to the movable, contact 213 there. are the: eightstationary contacts 299,,291, 292,293, 294,295, 296 and 29.1.. The contacts 286,281,, 28 8;and 2:89, andthe contacts 290, 29|, 292--and 293 are not used electrically, but are shown for uniformity of illustration. Also the; contacts 282,, 283, 284 and285 are connected together by the lead 298;, and the contacts 294., 295,. 296 211x129! arebconnected togctherby the lead. 29.9.. Also thecontacts 214 and 218 are connected to: gether and to, the 1eadq300; .thecontacts- 215. and 219 are connected together and. tothe lead 30-1; the contacts 2-16, and.28(l are. connectedtogether These resistances are connected, respectivelyto the leads 3%., 30],. 302 and 353,. and. theirother ends are. connected to the common lead- 388.

There is. provided the comparison resistance element 309'; and; one. end of this isconnected'to the lead 29l, and its other endis connected by the lead 3m to the lead308. r

There is. provided thelcurrent responsivekinstrument 3.1! suitable for. operation on alternating current. 1 One terminal of: thisinstrument is connected by the lead 312 tosthe'junctionofthe leads 398. and'3l0, and theother terminal of this instrument is. connected to the lead259, a

protective resistance 3.1 3 preferably being .in-'

troduced into this leadas shown; Thelead 2.9.8 (and-one. end of thecomparison resistance 309) connect to the: leads 258 and 26.8 by theleadzfi'ld. Thev leads 2411-, 248i and 24.9 of the cordto which the plug 249 isconnected, are connected respec tively-to the.;movableicontacts 213, 2.12 and 21!.

The lead2611from. the transformer Zed-connects to the lead 299 for the switch contact-a295, .295, 29Eand 291... A nullindica'tor: 315 isv provided,

, performinga functionsimilar tosthe function described; but inthe. present case this null indicator 315' is one WhiCh'lS capable of showing phase displacements as well as magnitudedifferences in the applied potentials; I shall'now explain this null indicator 3l5 ins'uflicient detail for the present purposes.

The nmr indicator illustrated consists "of a tothe attraction of the negatively charged electrons composing thebeam towards the'positive charge on the upper plate; The opposite o'r lower 'plate' may' be simultaneously subjected to i an equal negative charge by means of one'of several well known push-pull circuits, or may be maintained at. substantially fixed potential; the exact procedure varyingin various commercial forms of; the oscillograpll. Asecond pair ofde-lflection plates disposed at 90. degrees. to the 'v'e'r tical 'plat'esare capable, when subjected tosuit ableQeljectric. chargestof deflecting the'spotjto the right or the left in a. horizontal line. In most commercial forms bothv thev 1vertical andfithe horizontal'plates are subjected to appliedyolt-l ases hic e n m fie t us e1 tronic amplifiers; contained Within theIoscillo-,

nnea h a o these ampl fier is u al- 1y adjustable-by the operator-.;- I have illustrated one-form'of Such an oscilloscope herein asa null indicatort rm ct theconditiOnS impo ed by the use Of'alternating; current. sources, but in SQ- dOf i-ngI wish it; understood, that I do not intend to limit myself to such a form of null indicator, except as I may do so in the claims to follow.

In the circuit shown in Figure 6 the two vertical plates of the oscilloscope are shown at 3l6 and 3H, and the two horizontal plates are shown at 3|8 and 3l9. In the scheme shown in Figure 6 the vertical deflection plate 3!! and the horizontal deflection plate 318 are connected together by the lead 320, so these two plates are maintained at equal potential. Other methods of connection would be employed when the oscilloscope incorporated push-pull circuits to the deflection plates. In Figure 6 I have shown the amplifiers 321 and322 for the vertical and horizontal plates, such showing being by block diagram only since any one of several forms of amplifiers suitable to the present use. are commercially available.

The leads 249 and 2H are connected tothe lead 320 (and therefore to the plates 3!! and 3l8) by the lead 323; the plate 32! is connected to the lead M4 by the lead 324; and the plate 322 is connected to the junction point of the leads 308,3[ and 3l2 by the lead 325. "With this arrangement it will be seen that Whenever the movable contacts of the switch 210' are moved down to an operating position the vertical deflection plates 3I6 and 3H are connected across the two resistors 30! and 304 (or 305, 306 or 301') in series while the horizontal deflection plates 318 and 3l9 are connected across theresistor 304 (or 305, 306 or 301) alone. With this arrangement the following functions will occur:

So. long as the impedance of the resistance element or the reactance element under test is less than-infinity a current will flow through the resistance element 304 (or 305, 305 or 301) and there will be a voltage drop across this element. With an amplifier of suitablegain inthe horizontal deflection plate circuit a sufficient potential will be applied to the horizontal plates to obtain a movement of the spot horizontally across the screen. Then if the voltage drops across the resistance 304 (or 305, 306 or 301) and 309 are exactly equal and opposite, there will be'no poten-. tial impressed on the vertical plates, and no vertical movement of the spot will occur. This is the condition of exact balance desired, and this condition of exact balance Willbe indicated tothe operator by the production of a horizontal line on the screen. This condition also presupposes that the two voltages are exactly in phase. Now if the two voltages are exactly in phase but differ in magnitude the pattern will remain a straight line, but it will be tilted from the horizontal, and the manner of tilt,whether up towards the right, or down towards the right, will indicate whether the drop across the element 309 is-too great or too small in value, it being understood that the drop across this element is adjustable in amount similar to the adjustment of the element I35 shown in Figures 3, 4 and 5. If the voltages are equal in magnitude but differ in phase, such phase difference will be indicated by the fact that the straight line will assume an encesin magnitude, or in phase, and the operator may then proceed to make such corrections as may be required.

open form, comprisingan ellipse, and the length It is to be noted that the amplifiers serve to ensure suilicient magnitude of potentials across the plates of the null indicator to ensure an indication on .the screen of the oscilloscope, and the amount of gain of such amplifiers should be sufiicient to ensure a sufiicientamount of such deflection to enable easy examination of the indicator during various adjustments of the resistance and reactance elements of the network. Any harmonics present in the'alternating current sources, or introduced by non-linearity of the circuit elements, will be amplified by such amplifiers 32! and/or. 322, so that the line produced on the screen of the oscilloscope will indicate such harmonics, by departure of the line from a straight condition. However,'it is found that with some practice the operator is readily able to interpret the pattern on the screen accurately even when there are present harmonics of relatively high values. It is also notedthat the exact amount of gain of the amplifiers 32I and 322 is immaterial, as long as the pattern produced on the screen is of sufiicient magnitude toenable the operator to readily interpret the pattern. This fact is of importance in the present device since the gain of ordinary commercial amplifiers may be expected to vary with aging of their tubes, with variation in power supply voltage, and other factors.

The preferred method of adjustment of a typical resistance or reactance element (232 or 233) to the desired value, will consist in first adjusting the phase position of the source 254 to zero degrees (in the case of a resistance element) or to degrees (in the case of a reactance element), and then adjusting the magnitude of the voltage'by use of the switch25'l to obtain on the current responsive instrument 3 a deflection corresponding to the value of the resistance (or reactance) desired. This will generally produce a tilted pattern onthe screen of the null indicator. The resistance (or reactance) element is then adjusted to produce the desired horizontal linear pattern on the screen of the null indicator.

It will be evident-that in practice the current in the resistance 304' (or 305, 306 or 301) may not be-actually in phase with the voltage source 260 when adjustinga resistance element, nor in-exact quadrature when adjusting a reactance element. Such departure from exact phase for the adjustment of a resistance element will be due to reactance unavoidably included in the circuit, and such departure from exact quadrature for the adjustment of a reactance element will be due to the unavoidable inclusion of resistance in"'the circuit. These effects can be minimized by proper selection of circuit constants. Any errorremaining after reduction of these discrepancies by proper selection of circuit constants will not result in a false indication of the setting of the resistance (or reactance) being adjusted. This is because, once a null indication hasbeen obtainedthe magnitude of the drop across the: resistance 309 must be equal and opposite' tolthat across theresistor 304 (or 305, 306 or-301). If both are pure resistances, the currents inthem must bein exact opposition. These two: currents will therefore be additive algebraic'ally ratherthan geometrically, which'is the preferred condition for an accurate indication of the setting. of the element under adjustment by useof the instrument 3 H. if residual reactance is present when adjusting the resistance element, it is only necessarytoadjust the phase position of the source 254 on zero" by the proper amount to obtain a balance and no error is introduced. Likewise, if, when: adjusting a reactance element there be present residual; resistance; itis necessary to adjust. the phasezoi the source 254 oft quadrature: byuthe proper amount. Such adjustments are readily. made; and they do not impairthe accuracyof. the set:- lting or the resistance or. reactance element. then being. made. Frequently such a.djustments are .not needed at. allsince theunwanted. components of: reactance or resistance. .as the; case may .be. .areof; negligible valuesand do, not. afiectrthe pattern produced on. the screen of. thenullindicator-appreciably.

-, In; the. foregoing I have. spoken, of the; adjust.- mentof. the: resistance or reactance section of, a network element byimpressing acrossqthe'appropria-tejsection. a 1.0 per unit voltage; and b- .serving the deflection .of; a suitable current. re.- .sponsi-ve instrumentin series therewith. It will beappreciated that in adjusting. a section of. a network element. to a low .value of resistance: or reactance. the use 0i a 1.0 per unit voltage will result. in a large per unit. current which. may be.- comeexcessive as the-desired adjustmentbecomes. smaller... with consequent damage to; the equipment. Accordingly, it may be desirable to employ; a vvoltage smallerthan 1.0 per unit inany convenientratio. as. 0.1 .per'unit voltage. It will be understood that; any predetermined valueof voltage may-be used in accomplishing the adjust.-

ment providedonly that the scale ofthe current responsive-instrument is appropriately calibrated for. the voltage selected. v

The arrangements showninthe circuit. of. Fig.- ure-o maybe used not only for'ma-king the. adjustments of the various resistanceandreactance sectionsofthe elements of the .networkto values whichare correct for representation. of the values of corresponding elements of a real network, but may also be used for reading, currents in various branches of, the so-adiusted network. and its branches, and for measurement. of voltagesaat anypoint cf the network so; set up. These uses willnow bebriefiy: explained. r I

- In: Figure 8:1.have; shownin simplified form the elements used in. measuring current in, a. selected branch of: the miniature network, it: being understood. that currents in other branches may :be. measured by similar means and. operations. Uponinserting theplug 249 into: thesjack v2!! .onfl I: acircuit isestablished. through the tip and ring .contactsof suchjack, through the resistance element 304 (013051306 or 301); to the junction with the resistance 309; .Source 254' will produce acurrent' through'resist-ance element-309' to'this samejunction. The sum of these two currents will pass through the. current responsive-instrument-3i land source 254 to the-right hand end of resistance element 309', where'these two currents will separat'e, each returning to its source. The null indicator will indicate the necessaryadjustmerits needed in phase position and magnitude of the-voltage source 254, so that the operator may establish the desired balance by making such'ad- I 'j'ustm'ents. "I-he null condition "having been established the current responsive instrument 3| 1 will show the current flowing in thebranch under examination multiplied by a fixed constant, depending upon "the position of the switch 210 (which switch has not-been shown in Figures for sources as follows:

. Switch Position. r 'R .Rcadablcrange M311.

1up,marked IXl l 100 2 per unit I. to 10. Y per unitl;

. Zup,marked-PXt" 900 100 .4 per unit I: to 2.0,

I per unit.I..

- I 1 I perunltI. 1 down, markedFZXlW. 100- g 100 .05 per unit Z, to .01

, per unitZ.

2 down, marked Z .2. 900 100 .25 per unit Z-to .05

l per unit Z. 3 down, marked ZX .05. 3, 900 g 100 1.0 per unit Z to .20

. per unipz 4down-,markcdZ ;.0l 19,2000 100 6. .00 per unit Zsto.

' perunitZi purposes: of simplification or that I figure, only Byproviding an appropriate scale on. the instrument 3H this current may beread directly on such instrument. The phase position of the current then being measured in such branch. may be read directly from the phase position-of the volt.-

age irom-the source fid necessaryto obtain the null condition. Such phase position will be shown by the markings on the adjustment wheel used in the setting of the voltage source 250. The operator is thus able, by a single nulladjustment, to read both magnitude and phase position of the currentfin-any branch of the network by merely insertingthe plug 249 into the jack of the network element, and then making I the adjustments and tude by some'predetermined constant multiplier.

I have previously herein mentioned by way of illustration a set ofthe-values for r and R'which arelsatisfactory for giving certain values of I 1 /1 in calculating boards intended for operation on direct current sources. I now mention a setof values for the resistance elementstfld, 305,806 and 301, andfor the element 309; which]? have found satisfactory for use in calculating boards intended for operation on alternating current Base voltage, 1.0 per unit, 100 yolts. B'ase current, 1.0 per unit, 10 mil1iamp'eres=0.0l0 ampere.v Base impedance, 1 perrunit; 100 volts/0.10 ampere= l0,000 ohms. v

The foregoing values for the resistance {elements'3fl4, ans, cos. 307 and are are given merely unit: scales is from 0.02 to 10.00 over unit I -with full recognition of the fact that usual commercial 'movementsof the moving iron'typ'e are readable only-from 20% of full scale to full scale; I I

25. The range of impedance measurements with the milliammeter mentioned in (1) above is'from 5.0 per unit Zto 0.01 per unit Z using four scales.

3. Both item (1') and item (2) cover a range of-*500/1. Many calculating boards' currently 'in'operation are not capable of direct readings over so great a range. 4. The voltage drop across the resistance 3M (or'305, 306 or 30'!) and 309 takenone'at a time are in all cases between 2 volts and 20' volts.

These values are well adapted for use with the "available commercial forms of" cathode ray oscil- 

